OPTICAL ILLUSION is illustrated in Maggie Malone's 5,500 QUILT BLOCK DESIGNS, #465. It is dated back to the Silver Anniversary issue of "Farm Journal and Farmer's Wife" in 1945, according to Jinny Beyer's QUILTER'S ALBUM OF PATCHWORK PATTERNS, p.138-2. The "optical illusion" refers to the 3D effect created by dark and light, in this block, but also in many other geometric quilt patterns. The uniqueness of the pattern has more to do with the four rotating corner squares, because the four-point star in the center is most often set inside an octagon (see CARNIVAL), or else as the centerpiece of an 8-point star. Surprisingly, no other variation was found with a 6 x 6 grid, four point star like this, with four corner squares.
A classic optical illusion can be seen in the illustration left, adapted here from an article at Scientific American, and which demonstrates "12 Examples of Kenetic Illusions in Op Art." "Kenetic" means that the image seems to "move," though in reality the pattern is obviously static, although the eye itself moves as it scans the image, and thus creates the optics.
Other optical quilt motifs at this site include:
A THOUSAND PYRAMIDS
SUNSHINE AND SHADOW
ON THE SQUARE